Androgynous {\{101‾2{10\overline{1}2}}\} twin in zinc

Under ambient conditions, Zn is a hexagonal metal with a large $c/a$ ratio of 1.856. Plastic deformation is predominantly accommodated by basal $⟨a⟩$ slip and compression twins on the $\{$${10\overline{1}2}$$\}$ planes. Increasing hydrostatic pressure drastically reduces the $c/a$ ratio of Zn and, when a critical threshold of /=√3 at about 10 GPa is crossed, the $\{$${10\overline{1}2}$$\}$ twins are predicted to change from compressive to tensile in nature. What happens at the transition point, when $c/a=\sqrt{3}$, remains unknown. Here, we strain-cycle a textured polycrystalline sample of pure Zn at uniform hydrostatic pressures ranging between 2 and 17 GPa, over which the / ratio crosses the /=√3 compressive-tensile transition for $\{$${10\overline{1}2}$$\}$ twins. During deformation, the state of the sample is monitored in situ through x-ray diffraction to extract texture and internal strain evolution. By comparing the experimental results with the predictions of an elastoviscoplastic polycrystal simulation, we confirm the androgynous nature of $\{$${10\overline{1}2}$$\}$ twin response at low and high pressures. When $c/a=\sqrt{3}$, polycrystalline Zn does not display any evidence of twinning and its plastic behavior is controlled by mostly basal and pyramidal $⟨c+a⟩$ slip activity, with a very small contribution of prismatic $⟨a⟩$ slip. Evidence for the activity of other $\{$${10\overline{1}n}$$\}$ twinning modes, which have been suggested for Zn under high pressure, are not observed

Stress Balance in Synthetic Serpentinized Peridotites Deformed at Subduction Zone Pressures

Weak serpentine minerals affect the mechanical behavior of serpentinized peridotites at depth, and may play a significant role in deformation localization within subduction zones, at local or regional scale. Mixtures of olivine with 5, 10, 20 and 50 vol. % fraction of antigorite, proxies for serpentinized peridotites, were deformed in axial shortening geometry under high pressures (ca. 2–5 GPa) and moderate temperatures (ca. 350°C), with in situ stress and strain measurements using synchrotron X-rays. We evaluate the average partitioning of stresses at the grains scale within each phase (mineral) of the aggregate and compare with pure olivine aggregates in the same conditions. The in situ stress balance is different between low antigorite contents up to 10 vol. %, and higher contents above 20 vol. %. Microstructure and stress levels suggest the deformation mechanisms under these experimental conditions are akin to (semi)brittle and frictional processes. Unlike when close to dehydration temperatures, hardening of the aggregate is observed at low serpentine fractions, due to an increase in local stress concentrations. Below and above the 10–20 vol. % threshold, the stress state in the aggregate corresponds to friction laws already measured for pure olivine aggregates and pure antigorite aggregates respectively. As expected, the behavior of the two-phase aggregate does not evolve as calculated from simple iso-stress or iso-strain bounds, and calls for more advanced physical models of two-phase mixtures

Hydrogen and minor element incorporation in synthetic rutile

The solubility and incorporation mechanisms of H and various trivalent and divalent cations in synthetic rutile have been investigated. Experiments performed using different bulk Fe2O3 contents demonstrate that Fe3+ substitutes onto the main Ti site, charge-balanced by oxygen vacancies. Under more reducing conditions in Fe-poor systems, the concentration of Ti interstitials in rutile is increased,resulting in a decrease in H solubility. Variation in the solubility of different oxides in rutile as a function of ionic radius implies substitution onto the main Ti site, probably charge-balanced by oxygen vacancies. To a lesser degree, substitution of trivalent and divalent cations is locally charge-balanced by H incorporation. Variation in OH-stretching frequencies in infrared spectra as a function of composition implies that octahedral defects and structurally-incorporated H are coupled. However, in all samples, some of the H is also decoupled from substitutional impurities, as is evident from an OH-absorption band at 3279 cmÿ1. This band corresponds to the main OH band seen in spectra of many natural rutiles, implying that in most rutiles, H defects are decoupled from substitutional defects

P–V Equations of State and the relative stabilities of serpentine varieties

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System-on-Chip FPGA Devices for Complex Electrical Energy Systems Control

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High-Pressure Creep of Serpentine, Interseismic Deformation, and Initiation of Subduction

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Plasticity of the dense hydrous magnesium silicate phase A at subduction zones conditions

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Robust sensorless speed control purpose for induction motors

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